The present invention relates to a shift control system for an automatic transmission.
One conventional example of an electronic control system for an automatic transmission system employs sensors for, respectively, sensing vehicle speed and throttle opening and producing electric signals. In this conventional example, the transmission control system determines a transmission gear ratio corresponding to current values of the vehicle speed and throttle opening in accordance with one of predetermined shift patterns, which is selected by a manual operation of a driver of the vehicle or automatically.
However, this conventional control system is incapable of always providing a satisfactory control suitable to driver's intention because the gear ratio is determined simply by the vehicle speed and throttle opening, and there are, at most only about three different shift patterns available. In this conventional system, vehicle operating conditions other than the vehicle speed and throttle opening are not taken into account, and the shifting is restricted to few preset shift patterns. Therefore, the shift control of this system is inflexible. Furthermore, it requires much time and labor to design adequate shift patterns for many combinations of vehicles and engines.